1. Field of the Invention
The present invention relates in general to a process of generating cutter path data representative of a succession of discrete points which generally define a cutter path to be followed by a cutting tool or cutter for machining a workpiece. More particularly, the invention is concerned with improvements in the process of determining such discrete cutter path definition points.
2. Discussion of the Related Art
Generally, a manufacture of a desired part or product by machining a workpiece on an NC (numerically controlled) machine tool includes a CAD (computer aided design) data processing step, a CAM (computer aided manufacturing) data processing step, and an NC machining step, which are implemented in the order of description, as illustrated in FIG. 17.
In the CAD data processing step, part geometry data in the form of surface models and solid models which represent a desired cutting profile of the workpiece (i.e., a desired shape of the part) are generated according to commands generated by the operator of a CAD processor.
In the CAM data processing step, successive discrete points generally defining a cutter path are obtained by calculation on the basis of the part geometry data received by a CAM processor, so that a predetermined reference point of the cutter is moved through those discrete points in the subsequent NC machining step. The reference point of the cutter may be a center point of the cutter, for example. The cutter path defined by the discrete points (hereinafter referred to as "discrete cutter path definition points") is offset from the desired cutting profile of the workpiece by a distance determined by the cutter configuration, in the direction away from the desired cutting profile. For instance, the offset distance of the cutter path is determined by the radius of the cutter. In the CAM data processing step, cutter path data representative of the discrete cutter path definition points are then generated.
The CAM data processing step further includes a post-processing operation to convert the cutter path data to NC data (numerical control data) suitable for use in the subsequent NC machining step in which the workpiece is machined into the desired part. Generally, the NC data include cutter path data representative of the discrete cutter path definition points, and interpolation data indicative of either linear interpolation or circular interpolation of the adjacent discrete cutter path definition data. In the linear interpolation, the adjacent discrete points are connected by a straight segment. In the circular interpolation, the adjacent discrete points are connected by a circular arc segment.
In the NC machining step, the NC data are received by a numerical control device, which applies cutter motion commands to the numerically controlled or NC machine tool, so that the NC machine tool is operated to move the cutter along the cutter path according to the cutter motion commands, for thereby machining the workpiece to produce the part having the desired shape.
Thus, the series of steps to manufacture the desired part includes a data processing operation for generating the discrete cutter path definition points generally defining the path to be taken by the cutter. This data processing operation is implemented after the part geometry data are prepared and before the cutter motion commands are generated. In the example of FIG. 17, the data processing operation in question is the operation to obtain the discrete cutter path definition points by calculation in the CAM data processing step.
In the conventional CAM data processing step, the discrete cutter path definition points are determined on the basis of nominal profile or geometry of the part (desired cutting profile of the workpiece), and a predetermined tolerance which is a permissible maximum amount of deviation of the cutter path generally defined by the succession of discrete points, from a nominal cutter path which exactly follows the nominal part profile, as indicated in FIG. 19. The cutter path generally defined by the discrete points consists of straight segments which connect the adjacent discrete points. That is, the cutter path is approximated by the discrete points, so as to minimize the required volume of the cutter path data while assuring a minimum sufficient degree of NC machining accuracy of the workpiece (dimensional accuracy of the part manufactured).
If the tolerance used in determining the discrete cutting path definition points is made relatively small, the requirement for reducing the volume of the cutter path data may be satisfied while assuring a satisfactory degree of the NC machining accuracy. However, there are other requirements in the manufacture of a part by NC machining, such as a requirement for increased machining efficiency while assuring the satisfactory NC machining accuracy. A research conducted by the inventors of the present invention has indicated an importance of taking into account conditions associated with movement velocities of the cutter, even in the step of generating or determining the discrete cutter path definition points which are subsequently processed into the NC data used in the NC machining step.
In determining the discrete cutter path definition points, however, the conventional CAM data processing technique does not allow the operator to take into account the conditions other than the tolerance indicated above, such as the conditions associated with the movement velocities of the cutter. Thus, the conventional technique suffers from drawbacks arising from the incapability to satisfy the above requirements in the NC machining.